Art of manufacturing chin film driver circuits in the form of ICs (integrated circuits) has been applied to produce reliable yet low cost LCDs, image sensors, liquid crystal shutters and the like.
In one aspect the invention may improve manufacture yield for such ICs by forming such peripheral driver circuits on tile same substrate as the pixel electrodes so that connection terminals and external driver Ifs may be greatly reduced in number.
In another aspect tile invention may resolve a low reliability limitation pertinent to conventional process of IC manufacture which involves large area, high density bonding of IC elements.
In active matrix LCDs, for example, delay transfer circuit and output buffer circuitries included in a scanning circuit, which serves as a vertical drive circuit and hence an important element of a thin :Film driver circuit, are formed integrally with the pixel electrodes.
FIG. 1 shows a conventional scanning circuit, illustrating delay transfer circuit in an N-th stage 110 and N+1-st stage 120 of the circuit, each stage comprising 8 elements i.e. four pass transistors 101 and four inverters 102.
Such delay transfer circuit functions to transfer a received signal to the next-one with a prescribed delay in time. Thus, in this Figure, an input signal P to the delay transfer circuit of any one stage, the N-th stage 110, say, is transferred as the input P1 to the next stage, which is N+1-st stage in this example, a period of T later. This delay is a consequence of a shift operation of the corresponding delay transfer circuit in response to a clock pulse .PHI.1 and an inverted clock pulse .PHI.1.
Associated with the shift operations of the registers, scanning signals S1 and S2 are derived from the corresponding delay transfer circuit via respective buffer circuitries 111 and 121.
FIG. 2 shows a timing chart for the conventional scanning circuit of FIG. 1. It is seen that an output signal P2 coming out of the output terminal B of the stage N+1 is delayed from that of output signal P1 from the terminal A of the preceding stage N by a drive period (or clock period) T. It is noted that the scanning signals S1 and S2 have a scanning period Tv which is the same as clock period T.
As may be anticipated from the above example, such conventional scanning circuit must occupy a relatively large area, since the circuit comprises as many as 8-elements in each delay transfer circuit. Furthermore, should one element become defective in any stage, scanning signals could not be correctly transferred any further, resulting in a defective picture on the display. From the point of reliability of the scanning circuit and hence the thin film drive circuit, this type of defect poses a serious problem, since it can happen without defect in pixel electrodes.
In addition, conventional scanning circuit cannot operate fast enough for high resolution displays which require much higher scanning speed. This is due to the fact that the scanning period of conventional scanning circuits is the same as the period of the clock.